1. Field of the Invention
This invention is directed to handling interrupts in a data processing system where communications may flow between system and subsystem or subsystem and subsystem as peer-to-peer communications. More particularly, the invention relates to handling interrupts in a peer-to-peer system more efficiently to reduce total system latency.
2. Description of Prior Art
Interrupt handling in a data processing system on a peer-to-peer basis is performed in the IBM PS/2 computers and is described in the IBM Personal System/2 Hardware Interface Technical Reference manual in the Move Mode subsection of the Subsystem Control Block Architecture section, at pages 1-16 to 1-17, 1-29 to 1-32 and 2-5 to 2-8 (January, 1991). The PS/2 interrupt handling system advanced the art by providing the ability for subsystems to interrupt each other and communicate with each other without intervention by the system unit. In effect, the communication responsibility between subsystem units was moved from the main system unit to the subsystem units.
Each subsystem unit was given a bus master processor that arbitrated for control of the system bus with the main system unit and bus masters on all the other subsystem units or adapter cards. When a bus master was granted access to the bus, it sent an interrupt and a communication signal to the unit (system or subsystem) it wished to communicate with. The receiving unit would detect the interrupt and then search its memory for receipt of a signal message from the sending unit. Only one interrupt can be processed at a time in a given receiving unit. Also, the receiving unit must search its memory to determine which sending unit is requesting communication with it. Accordingly, there is some system latency in handling one interrupt at a time and searching memory to identify the source of the interrupt.